Mobility and wideband have become a development trend of modern communication technologies. The 3rd Generation Partnership Project (3GPP) has been devoted to long Term Evolution (LTE) system evolving from a 3G system with the aim of developing the 3GPP radio access technologies toward a high data ratio, a short delay, and optimized packet data applications. The Multi-input Multi-Output (MIMO) technology at the physical layer has become one of crucial technologies in the current mobile communication system due to a number of advantages thereof, for example, the capacity of the system is extended through space division multiplexing of multiple antennas, the throughput of the system is improved using a multiplexing gain of multiple antennas, and etc.
After a base station obtains some Channel State Information (CSI) (which can be an instantaneous value, or can be short-term or middle-to-long-term statistic information), it can optimize power, rates, and even transmitting directions applied to respective data streams in some preprocessing scheme, and possibly a part or all of interference between the data streams may be eliminated in advance at a terminal through preprocessing, thus achieving higher performance. However there is such a significant overhead of downlink MIMO feedback at present that no corresponding gain in performance can be achieved particularly in transmission at a high rank (i.e., the number of downlink transmission layers). Furthermore the performance of the existing codebook design is greatly degraded in the scenario of mobility at a high speed, so the efficiency of transmission cannot be guaranteed.
Accordingly it is highly desirable in the industry to lower signaling overhead of the terminal providing feedback of CSI.